Proto - planetary nebula OH231.8+4.2 dans la Poupe/HST

Proto - planetary nebula OH231.8+4.2 dans la Poupe/HST - Stars like our Sun will eventually expel most of their material out into a planetary nebula. This is in the process of happening to an object called OH231.8+4.2 - a proto - planetary nebula surrounding a cool and dying star. The system is better known as the Calabash Nebula because of its peculiar shape. Another nickname for this object - the Rotten Egg Nebula - is derived from the large amount of sulphur compounds present, . The nebula is composed of gas ejected by the central star and subsequently accelerated in opposite directions. The gas (colored yellow in the image) has reached tremendous velocities of up to one and a half million kilometers per hour. The ejection process is so efficient that most of the stellar mass is now contained in these bipolar gas structures. A team of Spanish and American astronomers has used the NASA/ESA Hubble Space Telescope to study how the gas stream rams into the surrounding material (shown in blue). Such interactions are believed to dominate the formation process in planetary nebulae. Due to the high speed of the gas, shock - fronts are formed on impact and these heat the surrounding gas. Although computer calculations have predicted the existence and structure of such shocks for some time, the observational evidence has so far been poor. This Hubble image reveals the shocks in impressive detail. Using filters that only let through light from ionised hydrogen and nitrogen atoms, astronomers have been able to distinguish the warmest parts of the gas heated by the violent shocks and have found that they form a complex double - bubble shape. The bright yellow - orange colours in the picture show how the high - speed gas is flowing from the star - like two supersonic speeding bullets ripping through a medium in opposite directions. The central star itself is hidden in the dusty band at the centr